With the rapid development of technology in scene visualization and computer graphics, there are various ways to display digital terrain images in real time referenced relative to the travel of an aircraft over a terrain. Flight displays require depiction of large terrain areas. Further, each scene (of a terrain) may contain millions of polygons in order to provide a safe flight display with high fidelity digital terrain depictions. Consequently, depiction of such a scene in real time with a large amount of terrain data often exceeds capacities of currently available systems.
Various methods for reducing resolution have been utilized in order to reduce the amount of terrain data for a particular depiction of data within the larger database. One of the most commonly used methods to reduce resolution may be a level of detail (LOD) method or variation of the LOD method. Generally, the main focus of the LOD method has been a reduction of the total number of polygons displayed on the screen at any point in time. Sub-sampled data is displayed, depending only on a distance from a viewpoint. The LOD method has been favored since it is simple and predictable. It also increases frame rates while maintaining local precision due to polygon reduction. (The frame rate is the number of frames or images that are projected or displayed per second. The higher the number of frames playing per second, the smoother the video playback appears to the user.)
Referring now to FIGS. 1-2, exemplary images of a terrain area are shown wherein a LOD method is used for selecting a level of the terrain grid. In FIG. 1, the top view of the exemplary terrain image is shown. In FIG. 2, the perspective view of the exemplary terrain image is shown. The LOD approaches tend to lose distinguishable features in the distance since the reduction in detail is not directly correlated to what is resolvable by a viewer (e.g. a pilot). As such, the LOD method may not achieve the optimal polygon reduction since the level of detail does not take actual elevation data into account. Moreover, it is impossible to generate error bounds (an error bound is an approximate error of each polygon representation) correctly since some data is discarded based on a viewpoint only.
Another example of the method to reduce resolution of terrain data may be a visibility preprocessing method such as Delauney algorithm. The visibility preprocessing method may increase the performance of the display system when it is used with the LOD method. However the method requires preprocessing of terrain data for runtime optimizations. Furthermore, its approach is usually based on a geometric error, which does not take the position of a viewer into account. The visibility preprocessing method may not differentiate a significant terrain area from a non-significant terrain area. For example, a mountain close to an aircraft may be regarded as a significant terrain area, requiring a detailed geometry for a safe terrain depiction.
Therefore, it would be desirable to provide a system and methods that overcome the drawbacks of existing terrain rendering methods and provide a safe visual representation of terrain data in real time, given limited capacity of the display system. It would be also desirable to provide a system and method allowing a user to determine the scale of the application based on hardware platforms, or to deterministically provide frame rates while maximizing precision. Deterministic frame rate is useful to maintain a consistent scene flow-rate.